JP3748482B2

JP3748482B2 - Image processing apparatus, method, and recording medium

Info

Publication number: JP3748482B2
Application number: JP25205197A
Authority: JP
Inventors: 利幸水野
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1997-09-17
Filing date: 1997-09-17
Publication date: 2006-02-22
Anticipated expiration: 2017-09-17
Also published as: JPH1198371A

Description

【０００１】
【発明の属する技術分野】
本発明は、環境光を測定する環境光測定装置および環境光測定結果に応じて演色性を求める画像処理装置、方法および記録媒体に関する。
【０００２】
【従来の技術】
撮像データや原稿データをコンピュータに取り込みＣＲＴなどのカラーディスプレイ画面上に表示し、必要なデザインや色変更を加えた後にプリンタなどに出力しハードコピーを得ることが一般でも多く行われる様になってきた。
【０００３】
そして、表示画像とハードコピーの色を合わせるべく、カラーマッチング処理が行われている。このカラーマッチング処理では、デバイスに応じた色信号間の変換、例えばＣＲＴに応じたＲＧＢ信号からプリンタに応じたＣＭＹＢｋ信号間の変換、を国際標準委員会（ＣＩＥ）で定められているデバイスに依存しない色空間（例えばＸＹＺ等）を介して行う。そして、各デバイスに応じた信号とデバイスに依存しない色空間との対応関係はプロファイルに変換テーブルとして格納されている。
【０００４】
例えば、プリンタのプロファイルは、目的のデバイスに種々の色画像データを与えて出力させた色画像を測色し、画像データと測色値を対応させたテーブルを作成することにより作成される。
【０００５】
これらのプロファイル作成時の環境照明光は図４のａ，ｂ曲線で示す様な分光分布を持ったＣＩＥで決められた標準照明光での値と仮定しているので、これらの照明下ではプロファイルにより正確に補正することができる。しかし、観察している環境照明光が図４のｃ，ｄ曲線で示す様な分光分布を持った照明下では正確に補正することができない。
【０００６】
これは５５０ｎｍ波長付近の輝線による光で演色性が悪いためである。これらの演色性の悪い環境照明下では、同じプリンタ出力物でも色の変化率が異なるために、異なった色に見える。そこで従来は、厳密な色合わせを行う場合にはプロファイル作成時の標準照明光と環境照明光をほぼ同じにする事や、環境照明光の種類を測定して更に色補正プロセスを加える事を行っている。
【０００７】
【発明が解決しようとする課題】
ところがプロファイル作成時の標準照明と環境照明光を同じにする事は、高価な設備を用いて複雑な作業を行うことが必要となるので一般の事務所では困難である。また、観察する環境照明光を測定して色補正する従来方法では図７に示す様に可視域光（例えば波長３８０〜７８０ｎｍ）の３色、ＲＧＢ色感度を持った光検出器を用いて測定を行い、色温度や環境照明光を判定し、補正を行っている。ところが従来の３色で色温度を測定し補正する方法では、検出する波長範囲が広いため、輝線を有する蛍光灯光源等を識別することができないという問題があった。
【０００８】
この為に、改善された従来方法では輝線やフリッカー検出を行い、蛍光灯照明か、否かを判定している。ところが、事務所などで多くみられる照明は蛍光灯とそれ以外が混じった様々なもので、例えば図５に示すように、分光的な方法で測定すると屋外光の中に輝線の影響がはっきりと現れるので、蛍光灯照明と判定されてしまう。
【０００９】
しかし、蛍光灯照明として色画像処理を行っても再現色は不正確になる。また、蛍光灯の種類や使用された時間経過でも演色性は異なり同様に再現色は不正確になる。このため、正確な色再現を行う場合、時間的、コスト的に負荷のかかる分光的な測定方法を使用せざるを得なかった。
【００１０】
本発明は上述の点に鑑みてなされたものであり、本願第１の発明は色再現に影響を与える環境光の演色性を簡単に高精度に求めることができるようにすることを目的とする。
【００１１】
また、本願第２の発明は、環境光を簡単な構成で測定することができる環境光測定装置を提供することを目的とする。
【００１２】
【課題を解決するための手段】
上述の目的を達成するために、本発明は以下の構成を有することを特徴とする。
【００１３】
本願請求項１に記載された発明は、主たる分光感度特性が蛍光灯の主要輝線付近に感度を有する第１のセンサと、主たる分光感度特性が前記蛍光灯の主要輝線を含まない第２のセンサ及び第３のセンサと、前記第１のセンサ、前記第２のセンサ及び前記第３のセンサの総出力に対する、前記第２のセンサと前記第３のセンサそれぞれの出力比の差を求め、該求めた差に基づき、環境光の演色性を求める手段を有することを特徴とする。
【００１４】
本願請求項５に記載された発明は、主たる分光感度特性が蛍光灯の主要輝線である５４６ｎｍ波長付近感度を有する第１の光検出手段と、主たる分光感度特性が前記主要輝線を含まない６５０ｎｍより長い波長帯に感度有する第２の光検出手段と、主たる分光感度特性が前記主要輝線を含まない４８０ｎｍ付近に感度を有する第３の光検出手段と、前記第１の光検出手段、前記第２の光検出手段及び前記第３の光検出手段の総出力に対する、前記第２のセンサと前記第３のセンサそれぞれの出力比の差を求め、該求めた差に基づき、環境光の演色性を求める手段を有することを特徴とする。
【００１６】
【発明の実施の形態】
（実施形態１）
実施形態１にかかる色画像処理部の１例を図１に示す。図１では色画像処理部をプリンターやモニターに出力するシステムに適用している。
【００１７】
図１は本発明の実施例に関わる、色画像処理装置について画像データを入力し、プリンターやモニターに出力する場合に利用した、画像入出力装置のブロック構成例を表した物である。
【００１８】
０１は環境照明光で原画像１０や出力先のプリント３１、出力モニタ３２を照明している。１１は入力画像信号で標準の照明光で得られた、例えばＮＴＳＣのＲＧＢ信号の形で取り込まれた画像信号である。２０は色画像処理部で、画像信号を観察環境照明下での出力に適した信号とする処理を行う。この色画像処理部は入力信号に補正パラメータを用い濃度補正やγ補正を行い色度信号ＸＹＺに変換する入力信号処理部２１、色度信号に環境照明光情報などを加味して最適な補正を加える色補正処理部２２、色補正した信号Ｘ′、Ｙ′、Ｚ′をプリンタ出力に適した信号Ｃ、Ｍ、Ｙ、Ｂｋに変換するプリンタ色処理部２３、同じく信号Ｘ′、Ｙ′、Ｚ′をモニタ出力に適した信号Ｒ、Ｇ、Ｂ、に変換するモニタ色処理部２４等から構成され、全体は図示しないＣＰＵで制御される。
【００１９】
プリント物３１は、Ｃ、Ｍ、Ｙ、Ｂｋ信号３０に基づき図示しないプリンタ部によって形成され、表示画像はＲ、Ｇ、Ｂ信号に基づきＣＲＴ等のモニタ３２によって出力表示される。
【００２０】
色補正処理部２２は環境照明光補正処理部２２ａやスキャナ照明情報等から補正量信号を発する光源補正テーブル２２ｂ、そしてルックアップテーブル２２ｃ、等からなる。４０は環境照明光測定手段でプリント物３１やモニタ３２を照らす環境照明光０１を測定し照明光に応じたデータをメモリ４１に蓄えることができる。
【００２１】
環境照明光測定手段は図３に示すような分光感度特性を有するセンサが図２の様に配置されている。各センサはシリコンフォトセルと干渉フィルタの組み合わせにより選択された光が受光される構造となっている。光検出手段Ｇセンサは分光感度特性が蛍光灯の主要輝線の５４６ｎｍに最高感度を有し、光検出手段Ｂセンサは主要輝線を含まない４８５ｎｍに最高感度を有し、光検出手段Ｒセンサはもう一つの主要輝線を含まない６８０ｎｍに最高感度を有する。このような構成を取ることにより環境照明光の輝線波長部分の光強度と輝線を除いた波長部分の光強度を測定することができる。
【００２２】
なお上述のセンサでは波長選択フィルターはシリコンフォトセルと干渉フィルタの組み合わせを用いたが、コスト的には干渉フィルタと色フィルタの組み合わせ、もしくは色フィルタの組み合わせでも実現可能である。
【００２３】
４１は環境光特定手段で、明度、色温度、演色性を特定して色画像処理部２０へ信号として送る。
【００２４】
照明光源の特定方法は照明に含まれる輝線波長部分の緑色の明るさと輝線部を除く青色光明るさや赤色光明るさが図４や図５に示すように照明光源により大きく変わるので、輝線波長部分の明るさと輝線部以外の青色部、赤色部の出力を測定した後、それぞれの全体光量に対するそれらの比を算出し、更に、照明の明るさ等も加味し、予め環境光特定手段メモリに格納されている光源データと比較して明度、色温度、演色性を特定することになる。
【００２５】
図６は環境照明光測定手段の検出器３種の総出力に対する、検出手段Ｂの出力比（同図の横軸）と、検出手段Ｇと検出手段Ｒそれぞれの出力比の差（同図の縦軸）を環境光の変化に応じてプロットしたものである。
【００２６】
演色性は図６の縦軸の大きさで決まり、例えば、値が０．２以下であれば演色性が良いと判断し、値が０．４５以上であれば演色性が悪いと判断し、中間の０．２から０．４５であれば中間の演色性と判断する。図６の例では同じ蛍光灯照明でもＦ１点やＤ２点、Ｆ３点等に位置付けられ区分けされる。Ｆ１は普通の蛍光灯で演色性が悪く、Ｆ３は高演色性蛍光灯で演色性が良く、Ｄ２は普通の蛍光灯に昼の屋外光が混じった照明で中間の演色性と判断される。
【００２７】
色温度は図６の横軸の大きさで決まり、例えば、値が０．２以下であれば色温度が低く、０．２から０．３５の間は中間の色温度、０．３５以上は高い色温度と判断されグループ化される。図６の例では、Ａ１点が標準光源Ａで低い色温度、Ｆ３点が高演色性蛍光灯で中間の色温度、Ｄ１点が標準照明Ｄ６５で高い色温度と特定しグループ化される。
【００２８】
演色性や色温度は、この様に各々グループ化され、環境光特定手段からの演色性及び色温度の属性信号が色補正２２に送られ、それぞれのグループ化に合った係数が選択される。
【００２９】
尚、色温度は検出手段Ｂの代わりに公知の色温度計を用いグループ分けしてもよい。また、演色性や色温度を特定する閾値は各検出手段の特性に基づき設定される値であり、各検出手段の特性で異なる。
【００３０】
次に、図１を用いて動作を説明する。原画像１０は図示しないスキャナーで読みとられ、標準の照明で得られた入力画像信号１１としてＲＧＢ信号の形で取り込まれ、入力信号処理部２１で公知の濃度補正やγ補正が施され色度信号ＸＹＺに変換される。
【００３１】
そして、各デバイス間の色再現範囲の違いを調整する色空間圧縮処理がルックアップテーブルを用いて行われ色度信号ＸＦ、ＹＦ、ＺＦに変換される。
【００３２】
一方、環境光測定手段４０は原稿１０やプリント物３１を観察する環境照明光０１を測定し、環境照明光情報として蓄えてる。図示していないＣＰＵは測定した環境照明光情報に応じて、明度４２、色温度４３、演色性４４を特定し、予め実験で求められている外光補正テーブル部２２ｂから、補正すべき白色データの三原色ＲＷＧＷＢＷ信号を環境照明光補正処理部に送り、補正に使用される様にコントロールする。
【００３３】
照明光色温度と明るさの補正は基準白色点が変化するとみなして、例えば（ＶｏｎＫｒｉｅｓ）の色順応予測式を使用して求める。
【００３４】
フォン・クリースの方法はマトリックスを作成した標準照明光を例えば前述した蛍光灯照明で作成され、観察される環境照明光も同じ場合のプリント紙やモニタ白色点の三刺激値ＦＸ、ＦＹ、ＦＺより、公知の変換方法で求められる三原色ＦＲＦＧＦＢとし、標準と異なった環境光で照明されたプリント等の補正される値は三刺激値Ｘ′Ｙ′Ｚ′とするとフォン・クリースの式によれば以下のように表せる。
【００３５】
【外１】

【００３６】
ここで（Ｍ）は基本原色から定義される３×３のマトリックスで表せる常数で（Ｄ）は白色点のシフト量であり、以下の様に表せる。
【００３７】
【外２】

ここでＲｋ＝ＲＷ／ＦＲ
Ｇｋ＝ＧＷ／ＦＧ
Ｂｋ＝ＢＷ／ＦＢ
である。
【００３８】
更に、演色性の補正は演色性に応じた演色性変換マトリックスを使用して行う。これは補正の係数は、例えば、多数の色票を演色性の良い標準照明Ｄ６５で測色し、各色票のＸ１、Ｙ１、Ｚ１、を求め、次いで演色性グループを代表する光源で同じ色票を測色し、各色票の色度値Ｘ２、Ｙ２、Ｚ２を求め、多数の色度値から変換に最適な係数を３×３のマトリックスの形で最小二乗法で求めることにより得ることができる。メモリにはこの様にして作成された、各演色性に応じた変換の係数が蓄えられている。
【００３９】
当然ながら濃度（明度）や色域が再現出力範囲を越える物に対しては、公知の方法で更に補正を加えることも可能である。
【００４０】
この様な補正を加え色補正部で補正された三刺激値信号Ｘ′、Ｙ′、Ｚ′をプリンタ色処理部２３でプリンタ出力に適したＣ、Ｍ、Ｙ、Ｂｋ信号３０に変換し、モニタ色処理部２２ｃでモニタの表示に最適なＲ′、Ｇ′、Ｂ′に変換される。これらの変換は公知の方法を用いて行われ、出力画像としてのプリント物３１や、モニタ画像を得る。
【００４１】
この様な処理を行うことで標準照明光と比べて違う色に再現され、変動した環境照明光に合う様に補正される。
【００４２】
本実施形態では環境光測定手段の分光感度特性が蛍光灯の主要輝線の５４６ｎｍに最高感度を有する光検出手段Ｇと、最高感度が６８０ｎｍの赤色に感度を有する光検出手段Ｒと、最高感度が４８５ｎｍの赤色に感度を有する光検出手段Ｂとで構成されるようにしたが、最高感度波長は前記の波長に厳密に限定されるものではない。また、色温度特定手段を別に設けるか、最高感度が４９０ｎｍの青色に感度を有する光検出手段Ｒの代わりに色温度特定手段を設けても良い。この場合の色画像補正処理は上記実施形態とほとんど同じである。
【００４３】
また最高感度が４９０ｎｍの青色に感度を有する光検出手段Ｂの代わりに色温度特定手段を設けても可能であり、この場合は色温度をグループ化せずに補正を行い、演色性の特定は光検出手段Ｇと光検出手段Ｒの出力比で行うことになる。処理のプロセスと結果は上記実施形態とほぼ同じである。
【００４４】
以上述べた本実施形態によれば、環境照明光測定手段により照明光の変化に応じた明度、色温度、演色性が正確に特定することができ、環境照明光に応じた色補正を行うことができる。
【００４５】
よって、プロファイルデータを作成した標準照明光と観察する環境照明光が異なっても、入力画像に色味がマッチした出力画像を得ることができる。
【００４６】
＜他の実施形態＞
本発明は複数の機器（たとえばホストコンピュータ、インタフェース機器、リーダ、プリンタ等）から構成されるシステムに適用しても一つの機器（たとえば複写機、ファクシミリ装置）からなる装置に適用してもよい。
【００４７】
また前述した実施形態の機能を実現する様に各種のデバイスを動作させる様に該各種デバイスと接続された装置あるいはシステム内のコンピュータに、前記実施形態機能を実現するためのソフトウエアのプログラムコードを供給し、そのシステムあるいは装置のコンピュータ（ＣＰＵあるいはＭＰＵ）を格納されたプログラムに従って前記各種デバイスを動作させることによって実施したものも本発明の範疇に含まれる。
【００４８】
またこの場合、前記ソフトウエアのプログラムコード自体が前述した実施形態の機能を実現することになり、そのプログラムコード自体、及びそのプログラムコードをコンピュータに供給するための手段、例えばかかるプログラムコードを格納した記憶媒体は本発明を構成する。
【００４９】
かかるプログラムコードを格納する記憶媒体としては例えばフロッピーディスク、ハードディスク、光ディスク、光磁気ディスク、ＣＤ−ＲＯＭ、磁気テープ、不揮発性のメモリカード、ＲＯＭ等を用いることが出来る。
【００５０】
またコンピュータが供給されたプログラムコードを実行することにより、前述の実施形態の機能が実現されるだけではなく、そのプログラムコードがコンピュータにおいて稼働しているＯＳ（オペレーティングシステム）、あるいは他のアプリケーションソフト等と共同して前述の実施形態の機能が実現される場合にもかかるプログラムコードは本発明の実施形態に含まれることは言うまでもない。
【００５１】
更に供給されたプログラムコードが、コンピュータの機能拡張ボードやコンピュータに接続された機能拡張ユニットに備わるメモリに格納された後そのプログラムコードの指示に基づいてその機能拡張ボードや機能格納ユニットに備わるＣＰＵ等が実際の処理の一部または全部を行い、その処理によって前述した実施形態の機能が実現される場合も本発明に含まれることは言うまでもない。
【００５２】
【発明の効果】
本願第１の発明によれば色再現に影響を与える環境光の演色正を簡単に高精度に求めることができる。
【００５３】
また、本願第２の発明によれば、環境光を簡単な構成で測定することができる環境光測定装置を提供することができる。
【図面の簡単な説明】
【図１】画像処理装置の１例を示す図。
【図２】環境光測定手段の構成を示す図。
【図３】蛍光灯の相対分光強度と環境光測定手段の分光感度を示す図。
【図４】標準の照明光の相対分光強度を示す図。
【図５】蛍光灯に外光が混じった場合の相対分光強度を示す図。
【図６】環境光特定手段で色温度と演色性を特定を説明する図。
【図７】蛍光灯の相対分光強度と従来の環境測定手段の分光感度を示す図。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ambient light measurement device that measures ambient light, and an image processing device, a method, and a recording medium that obtain color rendering properties according to the ambient light measurement result.
[0002]
[Prior art]
Captured image data and document data are imported into a computer and displayed on a color display screen such as a CRT, and after making necessary design and color changes, they are output to a printer or the like to obtain a hard copy. It was.
[0003]
A color matching process is performed to match the color of the display image and the hard copy. In this color matching process, conversion between color signals according to devices, for example, conversion between RGB signals according to CRTs and CMYBk signals according to printers, depends on the device defined by the International Standards Committee (CIE). This is done through a color space that is not used (for example, XYZ). The correspondence between the signal corresponding to each device and the color space independent of the device is stored as a conversion table in the profile.
[0004]
For example, a printer profile is created by measuring a color image output by giving various color image data to a target device, and creating a table in which the image data and colorimetric values are associated with each other.
[0005]
Since the ambient illumination light at the time of creating these profiles is assumed to be a value with standard illumination light determined by the CIE having a spectral distribution as shown by curves a and b in FIG. Can be corrected more accurately. However, the ambient illumination light being observed cannot be accurately corrected under illumination having a spectral distribution as shown by the curves c and d in FIG.
[0006]
This is because the color rendering properties are poor due to the light emitted from the bright line near the wavelength of 550 nm. Under these environmental illuminations with poor color rendering properties, the same printer output appears different colors because the color change rate is different. Therefore, conventionally, when strict color matching is performed, the standard illumination light and the environmental illumination light at the time of profile creation are made almost the same, or the type of the environmental illumination light is measured and a color correction process is further added. ing.
[0007]
[Problems to be solved by the invention]
However, making the standard illumination and the ambient illumination light the same when creating a profile is difficult in a general office because it requires complicated work using expensive equipment. Further, in the conventional method of measuring the ambient illumination light to be observed and correcting the color, as shown in FIG. 7, measurement is performed using a photodetector having three colors of visible light (for example, wavelength 380 to 780 nm) and RGB color sensitivity. The color temperature and ambient illumination light are determined and corrected. However, the conventional method of measuring and correcting the color temperature with three colors has a problem that a fluorescent light source having a bright line cannot be identified because the wavelength range to be detected is wide.
[0008]
For this reason, in the improved conventional method, bright lines and flicker detection are performed to determine whether or not the illumination is a fluorescent lamp. However, the lighting often seen in offices is a mixture of fluorescent lamps and others. For example, as shown in FIG. 5, when measured by a spectroscopic method, the influence of bright lines in the outdoor light is obvious. Since it appears, it will be determined as fluorescent lamp illumination.
[0009]
However, even if color image processing is performed as fluorescent lamp illumination, the reproduced color is inaccurate. In addition, the color rendering properties differ depending on the type of fluorescent lamp and the time of use, and the reproduced color is also inaccurate. For this reason, when performing accurate color reproduction, it is necessary to use a spectroscopic measurement method that is time-consuming and costly.
[0010]
The present invention has been made in view of the above points, and an object of the first invention of the present application is to make it possible to easily and accurately obtain the color rendering properties of ambient light that affects color reproduction. .
[0011]
The second invention of the present application aims to provide an ambient light measuring device capable of measuring ambient light with a simple configuration.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is characterized by having the following configuration.
[0013]
The invention described in claim 1 includes a first sensor having a main spectral sensitivity characteristic in the vicinity of a main emission line of a fluorescent lamp, and a second sensor having a main spectral sensitivity characteristic not including the main emission line of the fluorescent lamp. and a third sensor determines the first sensor, the difference between the second sensor and the third to the total output of the sensor, the second sensor and the third sensor each output ratio, the It has a means for obtaining the color rendering property of ambient light based on the obtained difference .
[0014]
The invention according to claim 5 of the present application is the first photodetecting means having a sensitivity near the wavelength of 546 nm , whose main spectral sensitivity characteristic is the main emission line of a fluorescent lamp, and the main spectral sensitivity characteristic from 650 nm not including the main emission line. A second light detecting means having sensitivity in a long wavelength band, a third light detecting means having a main spectral sensitivity characteristic not including the main bright line and having a sensitivity in the vicinity of 480 nm, the first light detecting means, and the second light detecting means. The difference between the output ratios of the second sensor and the third sensor with respect to the total output of the light detection means and the third light detection means is obtained, and the color rendering property of the ambient light is determined based on the obtained difference. It has the means to obtain, It is characterized by the above-mentioned.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIG. 1 shows an example of a color image processing unit according to the first embodiment. In FIG. 1, the color image processing unit is applied to a system that outputs to a printer or a monitor.
[0017]
FIG. 1 shows an example of a block configuration of an image input / output device used when inputting image data to a color image processing apparatus and outputting it to a printer or monitor according to an embodiment of the present invention.
[0018]
01 illuminates the original image 10, the output destination print 31, and the output monitor 32 with ambient illumination light. Reference numeral 11 denotes an input image signal obtained with standard illumination light, for example, an image signal taken in the form of an NTSC RGB signal. Reference numeral 20 denotes a color image processing unit that performs processing for converting an image signal into a signal suitable for output under illumination in an observation environment. This color image processing unit uses the correction parameter for the input signal to perform density correction and γ correction, and converts it to the chromaticity signal XYZ. Optimum correction is performed by adding environmental illumination light information to the chromaticity signal. The color correction processing unit 22 to be added, the printer color processing unit 23 for converting the color corrected signals X ′, Y ′, and Z ′ into signals C, M, Y, and Bk suitable for printer output, and the signals X ′, Y ′, The monitor color processing unit 24 converts Z ′ into signals R, G, and B suitable for monitor output, and the whole is controlled by a CPU (not shown).
[0019]
The printed matter 31 is formed by a printer unit (not shown) based on the C, M, Y, and Bk signals 30, and the display image is output and displayed on a monitor 32 such as a CRT based on the R, G, and B signals.
[0020]
The color correction processing unit 22 includes an environment illumination light correction processing unit 22a, a light source correction table 22b that generates a correction amount signal from scanner illumination information, and a lookup table 22c. Reference numeral 40 denotes an ambient illumination light measuring unit that measures the ambient illumination light 01 that illuminates the printed matter 31 or the monitor 32 and stores data corresponding to the illumination light in the memory 41.
[0021]
As the environmental illumination light measuring means, sensors having spectral sensitivity characteristics as shown in FIG. 3 are arranged as shown in FIG. Each sensor has a structure for receiving light selected by a combination of a silicon photocell and an interference filter. The light detecting means G sensor has the highest spectral sensitivity characteristic at 546 nm of the main bright line of the fluorescent lamp, the light detecting means B sensor has the highest sensitivity at 485 nm not including the main bright line, and the light detecting means R sensor is already present. It has the highest sensitivity at 680 nm that does not contain one main emission line. By adopting such a configuration, it is possible to measure the light intensity of the bright line wavelength portion of the environmental illumination light and the light intensity of the wavelength portion excluding the bright line.
[0022]
In the above-described sensor, the wavelength selection filter uses a combination of a silicon photocell and an interference filter. However, in terms of cost, the wavelength selection filter can be realized by a combination of an interference filter and a color filter, or a combination of color filters.
[0023]
Reference numeral 41 denotes an ambient light specifying unit that specifies the lightness, color temperature, and color rendering properties and sends them to the color image processing unit 20 as a signal.
[0024]
The method of identifying the illumination light source is that the brightness of the bright line wavelength part included in the illumination and the blue light brightness and red light brightness excluding the bright line part greatly vary depending on the illumination light source as shown in FIG. 4 and FIG. After measuring the brightness of the light and the output of the blue and red parts other than the bright line part, the ratio of each to the total light quantity is calculated, and the brightness of the illumination is also taken into account and stored in the ambient light specifying means memory in advance The lightness, color temperature, and color rendering properties are specified in comparison with the light source data.
[0025]
FIG. 6 shows the output ratio of the detection means B (horizontal axis in the figure) to the total output of the three detectors of the ambient illumination light measurement means, and the difference between the output ratios of the detection means G and the detection means R (in the figure). The vertical axis) is plotted according to changes in ambient light.
[0026]
The color rendering property is determined by the size of the vertical axis in FIG. 6. For example, if the value is 0.2 or less, it is determined that the color rendering property is good, and if the value is 0.45 or more, the color rendering property is determined to be bad. If it is 0.2 to 0.45 in the middle, it is judged as intermediate color rendering. In the example of FIG. 6, even with the same fluorescent lamp illumination, it is positioned and divided at points F1, D2, and F3. F1 is a normal fluorescent lamp with poor color rendering, F3 is a high color rendering fluorescent lamp with good color rendering, and D2 is determined to be an intermediate color rendering with illumination in which ordinary outdoor light is mixed with daylight outdoor light.
[0027]
The color temperature is determined by the size of the horizontal axis in FIG. 6. For example, if the value is 0.2 or less, the color temperature is low, an intermediate color temperature between 0.2 and 0.35, and 0.35 or more. High color temperature is judged and grouped. In the example of FIG. 6, the standard light source A has a low color temperature at point A1, the F3 point has a high color rendering fluorescent lamp, an intermediate color temperature, and the D1 point has a high color temperature at standard illumination D65, and is grouped.
[0028]
The color rendering properties and color temperature are grouped in this way, and the color rendering property and color temperature attribute signals from the ambient light specifying means are sent to the color correction 22 to select coefficients suitable for each grouping.
[0029]
The color temperatures may be grouped using a known color thermometer instead of the detection means B. Further, the threshold value for specifying the color rendering properties and the color temperature is a value set based on the characteristics of each detection means, and differs depending on the characteristics of each detection means.
[0030]
Next, the operation will be described with reference to FIG. The original image 10 is read by a scanner (not shown), is captured in the form of RGB signals as an input image signal 11 obtained by standard illumination, and is subjected to known density correction and γ correction by an input signal processing unit 21 and chromaticity. It is converted into a signal XYZ.
[0031]
Then, color space compression processing for adjusting the difference in the color reproduction range between devices is performed using a lookup table, and converted into chromaticity signals XF, YF, and ZF.
[0032]
On the other hand, the ambient light measuring means 40 measures the ambient illumination light 01 for observing the document 10 or the printed matter 31, and stores it as ambient illumination light information. The CPU (not shown) specifies the brightness 42, the color temperature 43, and the color rendering 44 according to the measured ambient illumination light information, and the white data to be corrected from the external light correction table unit 22b obtained in advance through experiments. Are sent to the environmental illumination light correction processing unit and controlled to be used for correction.
[0033]
The correction of the illumination light color temperature and brightness is determined using the chromatic adaptation prediction formula of (VonKries), assuming that the reference white point changes.
[0034]
The von Kries method uses standard illumination light with a matrix created with, for example, the above-mentioned fluorescent lamp illumination, and the observed ambient illumination light is the same from the tristimulus values FX, FY, FZ of the printed paper and the monitor white point. Suppose that the three primary colors FRGFFB obtained by a known conversion method are used, and the corrected values of prints illuminated with ambient light different from the standard are tristimulus values X'Y'Z ' It can be expressed as
[0035]
[Outside 1]

[0036]
Here, (M) is a constant that can be expressed by a 3 × 3 matrix defined from the basic primary colors, and (D) is the amount of white point shift, which can be expressed as follows.
[0037]
[Outside 2]

Where Rk = RW / FR
Gk = GW / FG
Bk = BW / FB
It is.
[0038]
Further, the color rendering properties are corrected using a color rendering property conversion matrix corresponding to the color rendering properties. This is because, for example, the color coefficients of a large number of color charts are measured with standard illumination D65 with good color rendering properties, X1, Y1, and Z1 of each color chart are obtained, and then the same color chart with a light source that represents the color rendering group. Can be obtained by obtaining the chromaticity values X2, Y2, and Z2 of each color chart and obtaining the optimum coefficient for conversion from a large number of chromaticity values in the form of a 3 × 3 matrix by the least square method. . In the memory, conversion coefficients corresponding to each color rendering property created in this way are stored.
[0039]
Of course, it is also possible to further correct the density (brightness) and color gamut beyond the reproduction output range by a known method.
[0040]
The tristimulus value signals X ′, Y ′, Z ′ corrected by the color correction unit with such correction are converted into C, M, Y, Bk signals 30 suitable for printer output by the printer color processing unit 23, The monitor color processing unit 22c converts it into R ', G', and B 'that are optimal for monitor display. These conversions are performed using a known method, and a printed matter 31 as an output image and a monitor image are obtained.
[0041]
By performing such processing, a color different from that of the standard illumination light is reproduced, and correction is made so as to match the changed environment illumination light.
[0042]
In this embodiment, the spectral sensitivity characteristic of the ambient light measuring means is the light detecting means G having the highest sensitivity at 546 nm of the main bright line of the fluorescent lamp, the light detecting means R having the highest sensitivity of 680 nm in red, and the highest sensitivity. Although it is configured with the light detection means B having sensitivity to 485 nm red, the maximum sensitivity wavelength is not strictly limited to the above-mentioned wavelength. In addition, a color temperature specifying means may be provided separately, or a color temperature specifying means may be provided instead of the light detection means R having a sensitivity of blue with a maximum sensitivity of 490 nm. The color image correction process in this case is almost the same as in the above embodiment.
[0043]
It is also possible to provide a color temperature specifying means instead of the light detection means B having a maximum sensitivity of 490 nm in blue. In this case, the color temperature is corrected without grouping, and the color rendering property is specified. This is performed at the output ratio of the light detection means G and the light detection means R. The process and result of the processing are almost the same as in the above embodiment.
[0044]
According to the present embodiment described above, the brightness, color temperature, and color rendering properties according to the change of the illumination light can be accurately specified by the environment illumination light measuring unit, and the color correction according to the environment illumination light is performed. Can do.
[0045]
Therefore, even if the standard illumination light that created the profile data is different from the ambient illumination light to be observed, an output image whose color matches the input image can be obtained.
[0046]
<Other embodiments>
The present invention may be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.) or an apparatus composed of a single device (for example, a copying machine, a facsimile machine).
[0047]
In addition, a program code of software for realizing the functions of the embodiment is provided to an apparatus or a computer in the system connected to the various devices so as to operate the various devices so as to realize the functions of the above-described embodiments. What is implemented by operating the various devices according to a program stored in the computer (CPU or MPU) of the system or apparatus supplied is also included in the scope of the present invention.
[0048]
In this case, the software program code itself realizes the functions of the above-described embodiments, and the program code itself and means for supplying the program code to the computer, for example, the program code are stored. The storage medium constitutes the present invention.
[0049]
As a storage medium for storing the program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.
[0050]
Further, by executing the program code supplied by the computer, not only the functions of the above-described embodiments are realized, but also the OS (operating system) in which the program code is running on the computer, or other application software, etc. It goes without saying that the program code is also included in the embodiment of the present invention even when the functions of the above-described embodiment are realized in cooperation with the embodiment.
[0051]
Further, the supplied program code is stored in the memory provided in the function expansion board of the computer or the function expansion unit connected to the computer, and then the CPU provided in the function expansion board or function storage unit based on the instruction of the program code However, it is needless to say that the present invention also includes a case where the function of the above-described embodiment is realized by performing part or all of the actual processing.
[0052]
【The invention's effect】
According to the first invention of the present application, the color rendering correctness of the environmental light that affects the color reproduction can be easily obtained with high accuracy.
[0053]
In addition, according to the second invention of the present application, it is possible to provide an ambient light measurement device that can measure ambient light with a simple configuration.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of an image processing apparatus.
FIG. 2 is a diagram showing a configuration of ambient light measurement means.
FIG. 3 is a diagram showing the relative spectral intensity of a fluorescent lamp and the spectral sensitivity of an ambient light measuring unit.
FIG. 4 is a diagram showing the relative spectral intensity of standard illumination light.
FIG. 5 is a diagram showing a relative spectral intensity when external light is mixed in a fluorescent lamp.
FIG. 6 is a diagram for explaining identification of color temperature and color rendering by an ambient light identification unit;
FIG. 7 is a diagram showing the relative spectral intensity of a fluorescent lamp and the spectral sensitivity of a conventional environment measuring means.

Claims

A first sensor having a main spectral sensitivity characteristic in the vicinity of a main emission line of a fluorescent lamp;
A second sensor and a third sensor whose main spectral sensitivity characteristics do not include the main emission line of the fluorescent lamp;
A difference between output ratios of the second sensor and the third sensor with respect to a total output of the first sensor, the second sensor, and the third sensor is obtained, and an environment is determined based on the obtained difference. An image processing apparatus comprising means for obtaining a color rendering property of light.

The image processing apparatus according to claim 1, wherein the second sensor is a blue sensor that detects a blue component, and a red sensor that detects a red component of the third sensor .

The image processing apparatus according to claim 1, further performing color processing according to the color rendering properties of the ambient light.

The image processing apparatus according to claim 3, wherein the color processing performs chromatic adaptation conversion processing.

A first light detecting means having a spectral sensitivity characteristic having a sensitivity near a wavelength of 546 nm, which is a main emission line of a fluorescent lamp;
A second photodetecting means having a main spectral sensitivity characteristic sensitive to a wavelength band longer than 650 nm not including the main emission line;
A third photodetecting means whose main spectral sensitivity characteristic is sensitive around 480 nm not including the main emission line;
A difference between output ratios of the second sensor and the third sensor with respect to a total output of the first light detection means, the second light detection means, and the third light detection means is obtained, and the obtained value is obtained. An image processing apparatus comprising means for obtaining a color rendering property of ambient light based on the difference.

An output from the first sensor whose main spectral sensitivity characteristic is sensitive in the vicinity of the main bright line of the fluorescent lamp, and an output from the second sensor and the third sensor whose main spectral sensitivity characteristic does not include the main bright line of the fluorescent lamp Enter
A difference between output ratios of the second sensor and the third sensor with respect to a total output of the first sensor, the second sensor, and the third sensor is obtained, and an environment is determined based on the obtained difference. An image processing method comprising obtaining a color rendering property of light.

Output from the first photodetecting means having a sensitivity near 546 nm wavelength whose main spectral sensitivity characteristic is the main emission line of a fluorescent lamp, and a second spectral sensitivity characteristic having a sensitivity in a wavelength band longer than 650 nm not including the main emission line. The output from the light detection means and the output of the third light detection means having a sensitivity near 480 nm whose main spectral sensitivity characteristic does not include the main emission line,
A difference between output ratios of the second sensor and the third sensor with respect to a total output of the first light detection means, the second light detection means, and the third light detection means is obtained, and the obtained value is obtained. An image processing method comprising: obtaining a color rendering property of ambient light based on the difference.

A recording medium storing a program in a state readable by a computer,
An output from the first sensor whose main spectral sensitivity characteristic is sensitive in the vicinity of the main bright line of the fluorescent lamp, and an output from the second sensor and the third sensor whose main spectral sensitivity characteristic does not include the main bright line of the fluorescent lamp Enter
A difference between output ratios of the second sensor and the third sensor with respect to a total output of the first sensor, the second sensor, and the third sensor is obtained, and an environment is determined based on the obtained difference. A recording medium for recording a program for determining the color rendering properties of light.

A recording medium storing a program in a state readable by a computer,
Output from the first photodetecting means having a sensitivity near 546 nm wavelength whose main spectral sensitivity characteristic is the main emission line of a fluorescent lamp, and a second spectral sensitivity characteristic having a sensitivity in a wavelength band longer than 650 nm not including the main emission line. The output from the light detection means and the output of the third light detection means having a sensitivity near 480 nm whose main spectral sensitivity characteristic does not include the main emission line,
A difference between output ratios of the second sensor and the third sensor with respect to a total output of the first light detection means, the second light detection means, and the third light detection means is obtained, and the obtained value is obtained. A recording medium for recording a program for determining the color rendering of ambient light based on the difference.